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I have a symfony app with a Comment entity, and I would like to link it, with a relation property, to many entities. But by many entities, I don't mean many objects, but many classes.

A comment can be about different things in my app : a Drawing entity, a Texte entity, a Compo entity, or a Photo entity. Each entity correspond to a type of artwork, each one with differents properties and different pages. And each one can be rated and commented.

The problem is : when I wanna create the relation property in my Comment entity, I got to indicate just ONE entity. I want that some comments are about a drawing entity, some are about text etc.

I see a solution : create one entity comment by entity to be link, but my app would have very many entities, and my code would be so duplicated, which is not so good for future changes etc.

Is there a way to link one entity to many differents types of entity ?

Thank you.

EDIT 4 : ALL PREVIOUS EDITS BELOW ARE POINTLESS !

I let it so beginners can see some of my code, to have an inheritance mapping example detailed (I which I could have it when I tried first, I didn't understood everything) but I just realised the stupid mistake I made :

 * @DiscriminatorMap({"comment" = "Comment", "comment" = "CommentDrawing", "commentphoto" = "CommentPhoto", "commenttexte" = "CommentTexte"})
  • I forgot "commentcompo" = "CommentCompo"
  • I wrote "comment" = "Comment" AND "comment" = "CommentDrawing" (both referenced by "comment")

That's why I had to put "comment" as discriminator instead of "commentdrawing".

Sorry for that stupid mistake, So much code lines I didn't notice it.

And for those who also use inheritance mapping for first time and want informations, I'm now trying to fill comments with forms. If you want to do the same (you probably will if you came here for an answer), I think this is the solution :

https://symfony.com/doc/current/form/inherit_data_option.html

EDIT :

Thanks to the answer of Jakumi below, I used inheritance mapping. I chosen the first solution : the one table solution. But I tried, I have no error message, but this didn't work to me, and after hours I still dont understand what I did wrong.

My Comment class (the topmost class of my comments hierarchy, which has CommentDrawing, CommentCompo, CommentPhoto, CommentTexte as children) (Comment is abstract because I had an error telling me that indicated me to put it abstract to solve the error) :

<?php namespace App\Entity; use App\Entity\Comment; use App\Entity\CommentPhoto; use App\Entity\CommentTexte; use App\Entity\CommentDrawing; use Doctrine\ORM\Mapping as ORM; use Doctrine\ORM\Mapping\InheritanceType; use Doctrine\ORM\Mapping\DiscriminatorMap; use Doctrine\ORM\Mapping\DiscriminatorColumn; /** * @ORM\Entity(repositoryClass="App\Repository\CommentRepository") * @InheritanceType("SINGLE_TABLE") * @DiscriminatorColumn(name="discriminator", type="string") * @DiscriminatorMap({"comment" = "Comment", "comment" = "CommentDrawing", "commentphoto" = "CommentPhoto", "commenttexte" = "CommentTexte"}) */ abstract class Comment { /** * @ORM\Id() * @ORM\GeneratedValue() * @ORM\Column(type="integer") */ private $id; /** * @ORM\Column(type="datetime") */ private $createdAt; /** * @ORM\Column(type="text") */ private $content; /** * @ORM\ManyToOne(targetEntity="App\Entity\User", inversedBy="comments") * @ORM\JoinColumn(nullable=false) */ private $author; public function getId(): ?int { return $this->id; } public function getCreatedAt(): ?\DateTimeInterface { return $this->createdAt; } public function setCreatedAt(\DateTimeInterface $createdAt): self { $this->createdAt = $createdAt; return $this; } public function getContent(): ?string { return $this->content; } public function setContent(string $content): self { $this->content = $content; return $this; } public function getAuthor(): ?User { return $this->author; } public function setAuthor(?User $author): self { $this->author = $author; return $this; } }

And here is my CommentDrawing entity (I created the other CommentSomething classes but the only one I tried to use now is CommentDrawing) :

<?php namespace App\Entity; use App\Entity\Comment; use Doctrine\ORM\Mapping as ORM; /** * @ORM\Entity(repositoryClass="App\Repository\CommentDrawingRepository") */ class CommentDrawing extends Comment { /** * @ORM\Id() * @ORM\GeneratedValue() * @ORM\Column(type="integer") */ private $id; /** * @ORM\ManyToOne(targetEntity="App\Entity\Dessin", inversedBy="commentsDrawing") */ private $drawing; public function getId(): ?int { return $this->id; } public function getDrawing(): ?Dessin { return $this->drawing; } public function setDrawing(?Dessin $drawing): self { $this->drawing = $drawing; return $this; } }

And here is the Dessin entity it refers to (dessin is drawing in french, I forgot to name it with english name when I created it) this is not a child class of Comment, this is the subject of the CommentDrawing (linked by ManyToOne), which is itself the child class of Comment :

<?php namespace App\Entity; use Cocur\Slugify\Slugify; use Doctrine\ORM\Mapping as ORM; use Doctrine\Common\Collections\Collection; use Doctrine\Common\Collections\ArrayCollection; use Symfony\Component\Validator\Constraints as Assert; use Symfony\Bridge\Doctrine\Validator\Constraints\UniqueEntity; /** * @ORM\Entity(repositoryClass="App\Repository\DessinRepository") * @ORM\HasLifecycleCallbacks * @UniqueEntity( * fields = {"nom"}, * message = "Un autre dessin contient le même nom. Merci de le changer. Vérifiez aussi que vous avez entré un slug unique, ou vide. Si le slug est en double, ça engendrera un bug.") * @UniqueEntity( * fields = {"url"}, * message = "Un autre dessin contient la même url, vous vous apprêtez à poster deux fois le même dessin. Merci de changer l'url.") * ) */ class Dessin { /** * @ORM\Id() * @ORM\GeneratedValue() * @ORM\Column(type="integer") */ private $id; // Some code I hidden because it's useless to show /** * @ORM\Column(type="string", length=255) */ private $slug; // Some code I hidden because it's useless to show /** * @ORM\OneToMany(targetEntity="App\Entity\CommentDrawing", mappedBy="drawing") */ private $commentsDrawing; public function __construct() { // Some code I hidden $this->commentsDrawing = new ArrayCollection(); } // Some code I hidden public function getId(): ?int { return $this->id; } // Some code I hidden public function getSlug(): ?string { return $this->slug; } public function setSlug(string $slug): self { $this->slug = $slug; return $this; } // Some code I hidden /** * @return Collection|CommentDrawing[] */ public function getCommentsDrawing(): Collection { return $this->commentsDrawing; } public function addCommentsDrawing(CommentDrawing $commentsDrawing): self { if (!$this->commentsDrawing->contains($commentsDrawing)) { $this->commentsDrawing[] = $commentsDrawing; $commentsDrawing->setDrawing($this); } return $this; } public function removeCommentsDrawing(CommentDrawing $commentsDrawing): self { if ($this->commentsDrawing->contains($commentsDrawing)) { $this->commentsDrawing->removeElement($commentsDrawing); // set the owning side to null (unless already changed) if ($commentsDrawing->getDrawing() === $this) { $commentsDrawing->setDrawing(null); } } return $this; } }

To verify if this worked correctly, I manually created a comment in the database with phpmyadmin :

comment in phpmyadmin

Then I tried to show the content of the drawing comment above in a page, using the drawing var corresponding to the drawing which is the subject of my comment. Nothing happened. So I directly tried to dump it in a Controller, impossible to get the comment.

To get the comment, I used the $commentsDrawing property of Drawing entity (you can see it in the code above). Here is the code I used to dump the drawing var that should contain a comment (I put the dump() function in the show function, that is call with the drawing slug as parameter, founded in the URL. I'm sure the show() function works correctly and show the good drawing, because I tested it before). It is the DrawingController :

<?php namespace App\Controller; use App\Entity\Dessin; use App\Form\DrawingType; use App\Entity\CategorieDessin; use App\Service\PaginationService; use App\Repository\DessinRepository; use App\Repository\CategorieDessinRepository; use Symfony\Component\HttpFoundation\Request; use Doctrine\Common\Persistence\ObjectManager; use Symfony\Component\HttpFoundation\Response; use Symfony\Component\Routing\Annotation\Route; use Sensio\Bundle\FrameworkExtraBundle\Configuration\IsGranted; use Symfony\Bundle\FrameworkBundle\Controller\AbstractController; class DrawingsController extends AbstractController { // I hide the rest of the code because it's useless /** * show a drawing * * @Route("/dessin/{slug}", name="drawing_show") * * @return Response */ public function show(Dessin $drawing) { dump($drawing); die(); return $this->render('drawings/show.html.twig', [ 'drawing' => $drawing ]); } }

What the dump() shows :

result of dump on drawing

As you can see, in commentsdrawing > collection, no elements.

If I do the same without the dump(), I got the drawing, no error, but no comments neither.

I really don't see what I did wrong... Could someone please help ?

EDIT 2 :

When I do this :

/** * show a drawing * * @Route("/dessin/{slug}", name="drawing_show") * * @return Response */ public function show(Dessin $drawing, CommentDrawingRepository $repo) { $comments = $repo->findAll(); dump($comments); die(); return $this->render('drawings/show.html.twig', [ 'drawing' => $drawing ]); }

I get an empty array

EDIT 3 :

Well, I added a new CommentDrawing directly from my DrawingController :

/** * show a drawing * * @Route("/dessin/{slug}", name="drawing_show") * * @return Response */ public function show(Dessin $drawing, CommentDrawingRepository $repo, DessinRepository $repoDrawing, UserRepository $repoUser, ObjectManager $manager) { $drawing = $repoDrawing->findAll()[0]; $user = $repoUser->findAll()[0]; $comment = new CommentDrawing(); $comment->setCreatedAt(new \DateTime()) ->setContent("un test") ->setAuthor($user) ->setDrawing($drawing); $manager->persist($comment); $manager->flush(); $comments = $repo->findAll(); dump($comments); return $this->render('drawings/show.html.twig', [ 'drawing' => $drawing ]); }

And that worked. The comment is registred in the database, the dump shows a comment, and the comment appear in my page.

I tried to understand why the comment added with phpmyadmin didn't work, and what a surprise : the difference between both comments is that the one added with phpmyadmin has commentdrawing as dicriminator value, and the one added by doctrine has just comment as value... Which is the value for the abstract class ! I thought the discriminator value was usefull to tell doctrine what column to consider, I don't understand anymore... But well, problem solved. Thank you for your help !

phpmyadmin

note : the second one is the one which worked... Why ?

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    I would make a base artwork class that has comments, and each type of artwork extends that class, @Jakumi has explained different ways to extend entities, but is suggesting different comment types. Logically speaking though, you have one comment type and many artwork types so artwork should be the extended entity, Commented Jun 13, 2019 at 20:10
  • Thank you for your answer. I already modified my whole code to make different kind of comments, so I'll try to manage this first, but if I can't I will try later with different kind of artwork, it makes sens. Commented Jun 13, 2019 at 20:39
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    @fred a PersistentCollection with initialized: false is a lazy-loaded collection that isn't loaded yet (usually), which actually doesn't give you any information at all about whether it works. call some function like ->toArray() on it (the non-initialized collection!), to trigger loading, then dump the parent object and/or collection ... or dump collection->toArray() ^^ Commented Jun 14, 2019 at 10:21
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    @fred also nice find with the inherit_data form option. I wasn't aware that existed... Commented Jun 14, 2019 at 10:32

2 Answers 2

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There is nothing that says you can't have multiple ManyToOne relationships within single entity. So it may not be as elegant and clean as inheritance mapping as suggested by Jakumi, but it works with little effort. I've done this in a project along the lines of what you describe with a single Comment entity that references multiple other entitys at the same time. For my Comment class, I have other entitys (Admission and Referral) that each point to multiple Comments, but Admission and Referral are otherwise nothing alike and so would not make sense for me to have each of them extend some abstract class (as suggested by Arleigh Hix in the comments to your question). My reasons for doing this are not relevant to your project, but it works well for me.

Comment class:

/** * @ORM\Entity */ class Comment { /** * @ORM\Column(type="text") */ private $comment; /** * @ORM\ManyToOne( * targetEntity="App\Entity\Referral", * inversedBy="comments" * ); */ private $referral; /** * @ORM\ManyToOne( * targetEntity="App\Entity\Admission", * inversedBy="comments" * ); */ private $admission; // getters and setters omitted }

Then of course my Admission entity (and very similarly my Referral entity) have the other side of the relationship:

/** * @ORM\Entity */ class Admission { public function __construct() { $this->comments = new ArrayCollection(); } /** * @ORM\OneToMany(targetEntity="Comment", * mappedBy="admission", * ) */ private $comments; }
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tbh I actually thought about your solution as well and the only reason against it for me was, that it's not as searchable and technically you could have a single comment for two+ subjects (of different type). you could have mended all those problems with code (and an actually code-managed discriminator column) though. in fact, the table created is almost exactly the same as with single table inheritance (depending on discriminator column ^^). which is why I didn't go for it in the end ..... but the solution is good nevertheless.
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the association itself is most likely the wrong place to do this abstraction. Anyway, what you're probably somewhat looking for is inheritance mapping.

For reference:

https://www.doctrine-project.org/projects/doctrine-orm/en/2.6/reference/inheritance-mapping.html

one table solution:

One option would be, to do single table inheritance. Parent class gets a method "getSubject()" that the child classes override and holds userid + rating + comment text. Child classes are DrawingComment etc. and each of them has a one-to-one association to the comment's subject.

Advantages: simple, clear semantics, can distinguish by classname (or extra function/property) if need be, referential integrity is stable, somewhat easy to do stats over, searchable regardless of comment subject type

Disadvantages: discriminator-column is somewhat awkward to use and slightly reduces speed.

many tables solution:

Leave inheritance mapping, make abstract class (+ interface?) or trait (+interface) for the common code. store each comment type in its own class/entity/table. When you don't care about the type of a comment, you can still use interface functions to handle it cleanly.

advantages: same, as before - except for searchability, no discriminator column, since each comment type has its own table

disadvantages: searchability is slightly reduced

Ultimately it's a question of taste or habit. And it depends on the common and distinct fields of different comment types. if - apart from the subject - they all share the same fields, I would do single table inheritance. the more they differ, the more I'd tend towards the many tables solution.

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3 Comments

Thank you very much for that detailed and comprehensive response ! I'm reading all this, and I'll try it once I'm familiar with the concept.
I tried to use it the whole afternoon and evening, but I'm stuck. I can't get the comment from the drawing, so I'm not sure it worked, and I don't see what I could did wrong. I edited my first message to show the changes, the code and the problem. Any idea ?
@fred your discriminatormap is off, comment itself shouldn't be in it - if it is a somewhat abstract parent class - and two classes should not have the same value (Comment+CommentDrawing both have "comment"). secondly, the child classes should not duplicate fields (parent class should have its id as protected instead of private). Ehymels solution might be another alternative that is simpler.

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